DIFFERENT TYPES OF Well foundation & THEIR RELATIVE MERITS &DEMRITS

DIFFERENT TYPES OF Well foundation & THEIR RELATIVE MERITS &DEMRITS

1. Presentation on “ DIFFERENT TYPES OF Well foundation & THEIR RELATIVE MERITS &DEMRITS ” By A.ASARUDEEN (16MC02) M.E Structural Engineering PSG College of Technology Coimbatore CELL: 99944 61636

2. Well foundation is the most commonly adopted foundation for major bridges in India. Since then many major bridges across wide rivers have been founded on wells. Well foundation is preferable to pile foundation when foundation has to resist large lateral forces. introduction

3. Well foundations have been used in India for centuries. The famous Taj Mahal at Agra stands on well foundation. Introduction

4. To know the different types and shapes of well foundations . To know their relative merits and demerits. Objectives

5. Shapes of well foundations Wells have different shapes and accordingly they are named as:- Circular well, Double D well, Twin circular well, Double octagonal well, Rectangular well.

6. Shapes of well foundation .

7. types of well foundation

8. Open caisson are hollow chambers; The top and bottom of the caisson is open during construction. It may have any shape in plan . The caisson is sunk into place by removing the soil from the inside of the shaft until the bearing stratum is reached. . Open caisson or well :

9. Open caisson

10. Open caisson

11. The advantages of open caissons are their feasibility to be sunk to great depths. Their construction cost is relatively low . . A dvantages of Open caisson :

12. The disadvantages of the open caissons are that the bottom of the caisson cannot be thoroughly cleaned and inspected. The concrete seal placed in water is not satisfactory and soil near the cutting edge may require hand excavation by diver . If obstruction like boulders or logs are encountered the construction gets slowed down. . Disad vantages of Open caisson :

13. It has a working chamber at the bottom of the caisson which is kept dry by forcing out water under pressure, thus permitting excavation under dry conditions . . Pneumatic caisson :

14. As there is an access to the bottom of the caisson, obstruction can be easily removed. The soil can be inspected and the soil samples can be ,if required. Soil bearing capacity can be determined by conducting in-situ tests in the working chamber. Excavation and pouring of concrete is one in the dry. There is no settlement of the adjoining structures as the water table is not lowered. . Advantages of Pneumatic caisson :

15. Pneumatic caissons are highly expensive Pneumatic caisson should be used only when open caissons are not feasible. The penetration depth of below water table limited to 30 to 40 m. There is a lot inconvenience caused to the workmen while working under high pressure, the workers may develop caisson disease. In pneumatic caisson, large amount of manual work is required which increases the cost. . Disa dvantages of Pneumatic caisson :

16. Floating caissons are open at the top but closed at the bottom. These caissons are constructed on land and then transported to the site ,and floated to the place where these are to be finally installed. These are sunk at that place by filling them with sand, ballast, water or concrete to a levelled bearing surface. . Floating caisson :

17. Floating or Box caisson

18. . Floating or Box caisson

19. The installation of the floating caisson quick and convenient. As the floating caisson are prefabricated or precast, the quality of construction is good. Floating caisson are less expensive than open caissons. Floating caisson can be transported by floating at a relatively low cost. . Advantages of Floating caisson :

20. The load carrying capacity of a floating caisson is much lower than that of equivalent open caisson. The foundation bed has to be levelled before installation. The base of the floating caisson is to be protected against scour action. . Disad vantages of Floating caisson :

21. M.N Som. , S.C Das , Theory and practice of foundation design , Ashok.k.Ghosh,New Delhi,2006 . P.C.Varghese,Foundation Engineering, Ashok.k.Ghosh,New Delhi,2005 . Bowles, J.E. ,Foundation Analysis And Design(International Student Edition) , Mc-Greww hill,Singapore,1988 . Saha G.P. “Analysis and Design of Varanasi Bridge Well Foundations – A Conceptual Approach” Journal of Indian Roads Congress Vol. 54-2 . Paper presented in the Annual Session of IRC in November 1993. Referances .